A hard disk drive (HDD), also referred to as a “hard disk”, a “hard drive” or “fixed disk”, is a data storage device used for storing and retrieving digital information using one or more rapidly rotating disks or platters coated with magnetic material. The platters are paired with magnetic heads arranged on a moving actuator arm. The magnetic heads are configured to read and write data to the disk surfaces. When an HDD is in operation, each disk is rapidly rotated by a spindle system and data is read from and/or written to a disk using one or more read/write heads positioned over a specific location of the disk by the actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head and the surface of the disk must be tightly controlled. Current systems attempt to control head-media spacing or separation (HMS) between the head and disk surface so as to maintain head as close as possible to a rotating disk for effective operation of the HDD. As used herein, HMS generally refers to the total distance between the read/write head and the disk surface. HMS may include, for example, not only the flying height of the read/write head relative to the disk surface, but also thicknesses of all coating or lubrication layers on either of the read/write head or disk surface.
The HMS between a head and disk surface is a critical factor for determining the amount of information that can be written to and/or read from a disk, sometimes referred to as an areal bit density (number of bits/unit area on a disk surface). For example, as the separation between the head and the surface of the disk increases, the effectiveness of both reading data from and writing to the disk decreases. Thus, a larger HMS between the head and disk surface requires larger bit cells, thereby resulting in smaller areal density for recorded information. Conversely, a smaller HMS between the head and disk allows for smaller bit cells, thereby allowing for greater areal density for information recording. Increasing the areal density increases the total storage capacity of the disk drive, while decreasing the areal density decreases the total storage capacity.
There are existing systems that attempt to control the flying height of the read/write head so as to decrease the HMS for improving the operation of the HDD and increasing storage capacity. For example, some disk drives rely on an air bearing surface (ABS) configuration, wherein the separation between the read/write head and the disk is maintained as the result of the balance between the aerodynamic lift provided by the fast moving air generated by a disk's rotation, and the down force applied to a slider holding the head by the load beam portion of the actuator arm.
A further refinement to the ABS design is referred to as a thermal flying height control (TFC) design. In a TFC design, the slider includes an electrical resistor placed near the magnetic transducer of the head and, when activated, produces a temperature rise near the transducer causing the transducer to protrude towards the disk surface. Although the general flying height of the slider remains unchanged by the TFC, the magnetic transducer is brought even closer to the disk surface by several nanometers. When power to the heater is reduced or terminated, the heat quickly dissipates to the rest of the slider and the protrusion retracts. The cycle of heating and cooling can be repeated thousands of times per second. Although a TFC design allows for subtle movement of the head closer to the disk surface by a few nanometers, the TFC design relies on the flexible load beam and the ABS design, which generally acts over a range of hundreds of nanometers in the z-direction from the head to the disk surface.
Current systems and designs for controlling HMS between the read/write head and disk surface have shortcomings and thus impact overall performance of the HDD. For example, the ABS design fails to fully prevent contact between the head and disk surface during operation of the HDD. In particular, as part of the ABS design, the head area of the slider is gently urged toward the disk until contact is made (“touchdown”), at which point the slider is urged away from the disk (“pull-back”). Contact between the head and disk surface may also occur due to internal and external vibrations directly to the HDD, as well as the fluttering of the disk that may occur as a result of fluctuations in air flow within the HDD. The act of contacting the disk causes mechanical wear of the head which, over time, often leads to operational degradation and eventually failure. In order to guard against potential damage from intermittent contact with one another, the disk surfaces are generally coated with at least two layers; a first hard coating and a second lubricant coating. In addition, the heads themselves may also be coated with a hard coating to provide additional protection. Although the hard coatings and lubricant layers may provide protection, they also increase the HMS between the head and disk surface, thereby presenting a challenge when attempting to reduce HMS values and limiting the ability to increase areal densities for improving reading and storage capabilities.
Another drawback of the ABS design is the turbulence within the HDD as a result of high-speed air generated by the rotation of the disk. The air turbulence causes a “windage” effect, which can result in disk fluttering, as well as slight movement of the actuator arm, both of which can result in the head missing a desired track on the disk surface, commonly referred to as track miss-registration (TMR). Thus, TMR further reduces the reliability and performance of an HDD.